1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to digital rights management (DRM), and more particularly to certifying and controlling audio/video (A/V) signals which are output from an A/V device through an output terminal of a digital visual interface (DVI) or a high definition multimedia interface (HDMI), using DRM, wherein A/V signals are output according to a DRM rule of contents through certification of a relevant receiving device.
2. Description of the Prior Art
A conventional DRM technique encrypts contents so that only source devices having a license of the contents may play the contents. Another conventional DRM technique certifies and controls A/V signals transmitted/received between a source device and a sink device. Herein, the source device is a device for playing digital media and outputting A/V signals which are played, and the sink device is a device for simply receiving the A/V signals output from the source device and displaying the received A/V signals. For example, the source device may be a set-top box, a digital video disc (DVD) player, or a mainframe of a personal computer, and the sink device may be a digital television (TV), a liquid crystal display (LCD) monitor, or a plasma display panel (PDP) monitor.
Recently, studies have been actively progressing in regard to DRM, and commercial services employing DRM have been and continue to be introduced. The reason why DRM is utilized may be drawn from various characteristics which digital data have. Different from analog data, digital data have characteristics of being able to be copied without any loss, of being able to be reused and modified with ease, of being able to be easily distributed to a third person, and of permitting such copy and distribution to be performed easily at a very low cost. However, digital contents require a high cost, a great effort, and a long period of time to be manufactured. Therefore, if it is permitted to copy and distribute digital contents without permission, benefits of digital content manufacturers are infringed, thus depressing the creative will of digital content manufacturers and functioning as a large impeding factor in stimulating the digital content industry.
Efforts for protecting digital contents have been mostly concentrated on preventing a third person from accessing digital contents without permission. In other words, only some users having paid for digital contents are permitted to access the digital contents. Therefore, users which have paid can access digital contents which are not encrypted, but other users which have not paid cannot access such digital contents. However, if the users which have paid for access to the digital contents intentionally distribute the digital contents to a third person who has not paid for access to the digital contents, there is no way to prevent the third person from using the digital contents. In order to solve such a problem, DRM has been introduced. According to DRM, anyone may have access to encrypted digital contents without restriction, but a license for play is required in order to decrypt and play the encrypted digital contents. Therefore, when DRM is employed, it is possible to efficiently protect digital contents, in a way different from the prior art.
The concept of DRM will be described with reference to FIG. 1. DRM relates to how to handle contents (hereinafter, referred to as “encrypted contents”) protected by encryption, scrambling, or the like, and licenses to permit access to the protected contents.
Referring to FIG. 1, a DRM system includes a user 4 wanting to access contents protected by DRM, a content provider 1 providing the contents, a license issuer 2 issuing a license which includes right capable of accessing the contents, and a certification authority 3 issuing a certificate.
According to the DRM system, the user (content playing device) 4 may obtain desired contents from the content provider 1, where the obtained contents are encrypted contents which are protected by the DRM. Also, the user 4 may obtain a license allowing play of the encrypted contents from the license issuer 2. The user 4 having obtained the license can play the encrypted contents. Meanwhile, the certification authority 3 issues a certificate, which proves the user 4 to be a certified user, to the content provider 1 and the user. A certificate may be stored in a device of the user 4 when the device is manufactured. Also, when an available period of time of a certification is expired, another certificate may be reissued from the certification authority 3.
Recently, in order to satisfactorily enjoy digital media when A/V data are transmitted from a digital-media playing device to a display device, a DVI or a HDMI method has been mainly used for digital A/V channels for connecting the devices to each other.
In 1998, the Digital Display Working Group (DDWG) was formed under the necessity of a standardized digital video interface between a PC and a VGA monitor. DVI 1.0 specification released in 1999 was designed to transfer uncompressed digital video, and to support PC graphics resolutions beyond 1600×1200 and high definition television (HDTV) resolutions.
In 2003, the electronics industry started to use a DVI output as video outputs of DVD playing devices and satellite set-top boxes, and using a DVI input as video inputs of digital TVs, LCD monitors, and PDP monitors. Also, the DVI supports the High-bandwidth Digital Content Protection (HDCP) standard for detecting unauthorized copying of contents, the Extended Display Identification Data (EDID) standard, and the Display Data Channel (DDC) standard used to read the EDID.
The DVI uses transition-minimized differential signaling (TMDS). Eight bits of video data are converted to a 10-bit transition-minimized DC value, which is then serialized. A receiver deserializes received video data, and converts it back to eight bits. Therefore, to transfer digital RGB data requires three TMDS signals, and these three TMDS channels and one TMDS clock channel may be comprised in one TMDS link.
Although the DVI handles the transmission of uncompressed digital RGB video, the electronics industry felt the necessity of a smaller and more flexible solution based on the DVI technology. In April 2002, the HDMI working group was organized by Hitachi Ltd., Matsushita Electric Industrial Co., Ltd., Philips Electronics, Sony Corporation, and Thomson Multimedia.
The HDMI has advantages, such as addition of digital audio and support of consumer electronics control (CEC), as compared with the DVI. In addition, the HDMI permits five video cables and eight audio cables or more to be replaced with a single cable. Currently, HDMI inputs are also applied on digital televisions, LCD monitors, and PDP monitors. Through the use of an adapter cable, the HDMI can be compatible with a device using DVI.
Since the HDMI is designed on the basis of the DVI, the HDMI supports the HDCP standard, the EDID standard, and the DDC standard, similarly to the DVI. From the viewpoint of a video format, the HDMI supports RGB, 4:4:4 YCbCr, and 4:2:2 YCbCr and also supports a transmission rate up to 24 bits per pixel. From the viewpoint of an audio format, the HDMI can transfers uncompressed stereo audio streams and compressed audio streams. Therefore, DVD-Audio can be transferred digitally to a receiver through a single cable. Herein, ‘R’, ‘G’, and ‘B’ represent a red signal, a green signal, and a blue signal, respectively. Also, ‘Y’, ‘Cb’, and ‘Cr’ represent a luminance (brightness) signal, a blue chroma signal, and a red chroma signal, respectively.
FIG. 2 is a block diagram for explaining a transmitting/receiving process of A/V signals between a source device and a sink device using the DVI or the HDMI. Each of TMDS channels CH 0 to CH 2 can process either each of R, G, and B data or each of Y, Cb, and Cr data. The synchronization of A/V data is performed between the source device and the sink device through a separate TMDS clock channel. Also, a DDC is separately included in order to transmit EDID of the sink device to the source device. In the case of the HDMI, eight audio channels are included besides the video channels.
The source device, based on the DVI or the HDMI, can understand various information, such as the manufacturer ID, the product ID, and the serial number of the sink device, by checking the EDID included in the sink device. Also, the source device checks a video format or an audio format capable of being received in the sink device, and transmits A/V signals according to the checked formats.
Meanwhile, the DVI and the HDMI support the HDCP standard. Therefore, the source device encrypts A/V signals to be output by means of an HDCP scrambler, and the sink device receives and decrypts the encrypted A/V signals by means of an HDCP descrambler. Accordingly, only sink devices equipped with an HDCP descrambler capable of decrypting in a method corresponding to an encrypting method of a scrambler in a source device can receive A/V signals output from the source device. A sink device including no descrambler cannot obtain desired video or audio data from the source device, because either the source device blocks the transmission of the A/V signal to the sink device, or the sink device cannot decrypt the encrypted A/V signals although the A/V signals are transmitted to the sink device.
That is, an HDCP module makes it possible to prevent copy of data and outflow of data to a third-party device (that is, an unauthorized device) by encrypting and decrypting A/V data to be transmitted from a source device to a sink device.
FIG. 3 is a block diagram showing constructions of a conventional source device and a conventional sink device, each of which includes an HDCP module. A source device 100 is connected to a sink device 200 through DVI cables or HDMI cables. In the case in which the devices are connected to each other through the DVI cables, Y, Cb, and Cr channels and audio channels must be omitted in FIG. 3.
According to the DVI and the HDMI standard, high-speed serial digital transmission can be performed between a graphic host and a digital display apparatus, that is, between the source device 100 and the sink device 200, respectively. The DVI standard includes rules of a coding mode of the source device 100, a decrypting mode of the sink device 200, a signal transmitter (Tx) 160, and the electrical property of a signal receiver (Rx) 210, etc., and these rules are utilized in the present invention. The DVI and the HDMI standard also includes a rule of a communication control mode, that is, a DDC, which enables it possible for the source device 100 to read control data according to EDID standard stored in the sink device 200.
The source device 100 includes a data receiving unit 110, a media decrypter 120, an input interface 130, an audio modulator 140, the signal transmitter 160, an HDCP scrambler 150. The sink device 200 includes the signal receiver 210, an HDCP descrambler 220, an audio demodulator 230, an output interface 240, an EDID memory 250, a video output unit 260, and an audio output unit 270.
Multimedia contents provided from a content provider are received through data receiving unit 110, are decrypted in the media decrypter 120, such as an MPEG decrypter, to be converted into A/V data. Then, the A/V data are input into the input interface 130, so as to be converted into pixel data capable of being displayed on an actual screen and audio data capable of being heard.
Next, the pixel data are input into the signal transmitter 160, and the audio data are input into the signal transmitter 160 via the audio modulator 140 which modulates a frequency of the A/V data so that the sink device 200 may receive the A/V data.
The signal transmitter 160 encrypts the pixel data and the modulated audio data by means of the HDCP scrambler 150 accommodated in the signal transmitter 160, and then transmits the encrypted data to the sink device 200 through the respective corresponding channels.
The signal receiver 210 of the sink device 200 receives encrypted A/V signals through corresponding channels, decrypts the encrypted A/V signals by means of the HDCP descrambler 220, and thus outputs actual pixel data and modulated audio data. The pixel data are input into the output interface 240. The modulated audio data are demodulated by the audio demodulator 230 so as to be recovered to audio data of an audio frequency band, and then are input into the output interface 240.
The pixel data and the audio data, which have been input into the output interface 240, are transferred into the video output unit 260 and the audio output unit 270, respectively, thereby being output as video and audio which a user may see and hear.
According to the conventional DRM technology described above, it is possible to analyze the DRM rule of multimedia contents to which the DRM standard is applied through the certification of a source device, and to control the source device itself with respect to the use of the contents. However, the conventional DRM technology does not provide any method of enabling a content provider to certify and control that a sink device receives an A/V signal transmitted from a source device having a legal right.
Also, according to the conventional DRM method, it is impossible to control that data are transmitted to a source device although the data are contents in which the DRM rule is applied, so that it is difficult to differentially control each of the sink devices, and it is impossible to prevent illegal copying of A/V data output through a sink device.
Also, according to the conventional certification and control techniques of A/V signals, certification and control can be carried out between a source device and a sink device, that is, between two devices. However, such certification and control is performed regardless of the kind of contents, so that the conventional techniques cannot provide a certification function according to contents, such as giving certification of permitting the display of multimedia to a sink device according to contents, or as restricting some functions of a sink device according to contents.